Modelling the Stress-Settlement Behavior of Shallow Foundation in Unsaturated Sand Using Sigma/W and Plaxis

Zhong Han, Singyu Han, Won Teak Oh, Sai K. Vanapalli

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Unsaturated Soils

ABSTRACT: the Stress-Settlement Behavior of Shallow Foundation in Unsaturated Sand Using Sigma/W and Plaxis Zhong Han, Singyu Han, Won Teak Oh & Sai K. Vanapalli Department of Civil Engineering Œ University of Ottawa, Ottawa, Ontario, Canada ABSTRACT The stress versus settlement behavior of shallow foundations is significantly influenced by soil suction since it contributes to the changes in strength and stiffness of the subgrade soil. Oh and Vanapalli (2011) proposed a framework for modelling the stress versus settlement behavior of shallow foundations loaded in unsaturated soils taking account of the influence of soil suction using commercial finite element software, Sigma/W. In this paper, this framework is extended to model the stress versus settlement behavior of the same model footing tests using commercial finite element software, Plaxis. Comparisons are provided between the stress versus settlement behaviors obtained from model footing tests and from both the software. Discussions are also presented regarding the strengths and limitations of modeling the stress versus settlement behaviors of shallow foundations in unsaturated soils using finite element software, Sigma/W and Plaxis. RÉSUMÉ Le comportement de tassement en fonction de la contrainte appliquée pour des fondations superficielles est influencée de manière marquée par la succion puisqu'elle contribue aux changements de résistance et de rigidité du sol sous-jacent. Oh et Vanapalli (2011) on proposé un cadre conceptuel de modélisation du comportement de contrainte et déformation de fondations superficielles sur des sols non-saturés tenant compte de l'influence de la succion matricielle en utilisant le logiciel d'analyse par éléments finis Sigma/W. Dans le présent article, ce cadre conceptuel est appliqué en utilisant le logiciel Plaxis. Des comparaisons sont données entre les relations de contrainte et déformation obtenues à partir des deux logiciels. Une discussion est également présentée sur les forces et faiblesses de la modélisation du comportement de contrainte et déformation en utilisant les logiciels d'analyse par éléments finis Sigma/W et Plaxis.. 1 INTRODUCTION The stress versus settlement (hereafter referred to as SvS) behavior is the key information required in the design of shallow foundations. Reliable estimation of the SvS behavior is possible from constitutive relationships that can take into account of different loading scenarios as well as saturation conditions. The SvS behavior however is conventionally determined or estimated extending the mechanics of saturated soils. Use of such a procedure in practice is conservative for estimating the bearing capacity of soils required in the design of foundations. In many scenarios extending this procedure can lead to shallow foundations that are not economical. In addition, it is not reliable to estimate the settlement behavior of foundations using mechanics of saturated soils when the soil typically is in a state of unsaturated condition. Mechanics of saturated soils however is commonly used due to lack of a valid and simple framework for extending the mechanics of unsaturated soils in conventional geotechnical engineering practice (Oh and Vanapalli 2011). In recent years, several in-situ and laboratory experimental studies were reported in the literature that demonstrate significant influence of the soil suction on the SvS behavior of shallow foundations or model footings (e.g. Steensen-Bach et al. 1987, Oloo et al. 1997, Costa et al. 2003, Mohamed and Vanapalli 2006, Cicek et al. 2014). Vanapalli and Mohamed (2007) proposed a semi-empirical model to estimate ultimate bearing capacity (qult) of unsaturated soils extending Terzaghi (1943) bearing capacity equation for saturated soils based on model footing tests results in an unsaturated sand (Mohamed and Vanapalli 2006). For the same experimental results, Oh and Vanapalli (2011) proposed a methodology to simulate the SvS behavior of shallow foundations in unsaturated sand considering the influence of soil suction on the shear strength () and modulus of elasticity (Ei) using a commercial finite element software, Sigma/W. In the present study, following the framework proposed by Oh and Vanapalli (2011), another commercial finite element software, Plaxis is employed to simulate the SvS behavior of a model footing in an unsaturated sand using the same model footing tests results used by Oh and Vanapalli (2011) (i.e. Mohamed and Vanapalli 2006). Comparisons are provided between the measured SvS behaviors and those estimated using both Sigma/W and Plaxis. In addition, discussions are provided on the strengths and limitations of modeling the SvS behavior of shallow foundations in unsaturated soils using finite element software, Sigma/W and Plaxis. The studies summarized in this paper are expected to be useful for the practitioners to model the SvS behavior and estimate the bearing capacity and settlement behavior of shallow foundations installed in unsaturated soils.

RÉSUMÉ: ling the Stress-Settlement Behavior of Shallow Foundation in Unsaturated Sand Using Sigma/W and Plaxis Zhong Han, Singyu Han, Won Teak Oh & Sai K. Vanapalli Department of Civil Engineering Œ University of Ottawa, Ottawa, Ontario, Canada ABSTRACT The stress versus settlement behavior of shallow foundations is significantly influenced by soil suction since it contributes to the changes in strength and stiffness of the subgrade soil. Oh and Vanapalli (2011) proposed a framework for modelling the stress versus settlement behavior of shallow foundations loaded in unsaturated soils taking account of the influence of soil suction using commercial finite element software, Sigma/W. In this paper, this framework is extended to model the stress versus settlement behavior of the same model footing tests using commercial finite element software, Plaxis. Comparisons are provided between the stress versus settlement behaviors obtained from model footing tests and from both the software. Discussions are also presented regarding the strengths and limitations of modeling the stress versus settlement behaviors of shallow foundations in unsaturated soils using finite element software, Sigma/W and Plaxis. RÉSUMÉ

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Cite this article:
Zhong Han; Singyu Han; Won Teak Oh; Sai K. Vanapalli (2014) Modelling the Stress-Settlement Behavior of Shallow Foundation in Unsaturated Sand Using Sigma/W and Plaxis in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper346,author = Zhong Han; Singyu Han; Won Teak Oh; Sai K. Vanapalli,title = Modelling the Stress-Settlement Behavior of Shallow Foundation in Unsaturated Sand Using Sigma/W and Plaxis,year = 2014}